Sizing Up The Sexes

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What are little boys made of?

What are little boys made of?

Frogs and snails

And puppy dogs' tails,

That's what little boys are made of.

What are little girls made of?

What are little girls made of?

Sugar and spice

And all that's nice,

That's what little girls are made of.

-- Anonymous

Many scientists rely on elaborately complex and costly equipment to probe the mysteries confronting humankind. Not Melissa Hines. The UCLA behavioral scientist is hoping to solve one of life's oldest riddles with a toybox full of police cars, Lincoln Logs and Barbie dolls. For the past two years, Hines and her colleagues have tried to determine the origins of gender differences by capturing on videotape the squeals of delight, furrows of concentration and myriad decisions that children from 2 1/2 to 8 make while playing. Although both sexes play with all the toys available in Hines' laboratory, her work confirms what most parents (and more than a few aunts, uncles and nursery- school teachers) already know. As a group, the boys favor sports cars, fire trucks and Lincoln Logs, while the girls are drawn more often to dolls and kitchen toys.

But one batch of girls defies expectations and consistently prefers the boy toys. These youngsters have a rare genetic abnormality that caused them to produce elevated levels of testosterone, among other hormones, during their embryonic development. On average, they play with the same toys as the boys in the same ways and just as often. Could it be that the high levels of testosterone present in their bodies before birth have left a permanent imprint on their brains, affecting their later behavior? Or did their parents, knowing of their disorder, somehow subtly influence their choices? If the first explanation is true and biology determines the choice, Hines wonders, "Why would you evolve to want to play with a truck?"

Not so long ago, any career-minded researcher would have hesitated to ask such questions. During the feminist revolution of the 1970s, talk of inborn differences in the behavior of men and women was distinctly unfashionable, even taboo. Men dominated fields like architecture and engineering, it was argued, because of social, not hormonal, pressures. Women did the vast majority of society's child rearing because few other options were available to them. Once sexism was abolished, so the argument ran, the world would become a perfectly equitable, androgynous place, aside from a few anatomical details.

But biology has a funny way of confounding expectations. Rather than disappear, the evidence for innate sexual differences only began to mount. In medicine, researchers documented that heart disease strikes men at a younger age than it does women and that women have a more moderate physiological response to stress. Researchers found subtle neurological differences between the sexes both in the brain's structure and in its functioning. In addition, another generation of parents discovered that, despite their best efforts to give baseballs to their daughters and sewing kits to their sons, girls still flocked to dollhouses while boys clambered into tree forts. Perhaps nature is more important than nurture after all.